From the S&W site:
Model 640, MSRP $727, 23 ounces empty.
Model 642, MSRP $545, 15 ounces empty.
Model 686, MSRP $830, 35 ounces empty, 2.5" barrel.
Here you have the MSRP new and the weights of the guns in question. You need to figure out if the prices are right for your area...but they sound fair to me.
As far as carrying a steel gun in your pocket...I cannot even tolerate an Airweight like the 642 in my pocket. I believe that there is a lot to do with how your body is shaped, here. I am a bit overweight, and a pound of gun in a hip pocket tends to drag my jeans down. Others report doing this regularly without discomfort.
If this is going to be a gun to be carried a lot and shot little, I would go for the 642. I have a 442, and it is the most carried.
If you do not like shooting +p's out of it, you can shoot regular velocity ammo, or even go to milder wadcutter target loads.
There is a big range in the sizes and weights of the guns that you mention. You have a decision to make based upon what you intend to do the most, carry or home defense.
